Guys any help would be appreciated. Looking at a boat with twin 500 efi. 150 hours approximatley. However I noticed that the water bypass behind the thermostat appears to be really rusty and the top of the plenum looks rusty too. Only have seen pics so far going to look at boat tmmrw. Any thoughts? Probability of clogged water jackets in block/heads? I know valve springs are common and will do that this winter. Thanks for input.

I would want to get the exhaust pressure tested in any saltwater boat. If owner has allowed it to get this way I would be concerned about what other maintenance has been deferred or ignored.